Various techniques are known for creating three-dimensional images of a scene, i.e., images that include depth or distance information. Exemplary methods include time-of-flight, phase detection and triangulation. These techniques generally require that the image be scanned, for example by a laser beam, and depth data acquired point by point. It would be desirable in many applications, however, to acquire depth or distance information simultaneously over the entire image.
U.S. Pat. No. 5,200,793, which is incorporated herein by reference, describes a range-finding array camera, including a light source and a CCD or other detector array. An electro-optical modulator modulates both the illumination of the target scene by the light source and the light reflected back from the scene to the detector array, so that the illumination and the detected light have the same modulation pattern. As the modulation frequency is varied, a computer analyzes the intensity variation at each pixel of the array in order to determine the distance from the camera to the portion of the scene imaged by the pixel.
S. Christie, et al., in Measurement Science and Technology 6 (September, 1995), pages 1301-1308, which is incorporated herein by reference, describe a two-dimensional ranging sensor system. This system includes a laser, to illuminate the scene of interest, and a gated, intensified CCD camera, which acquires an image of the scene. The laser is modulated to provide an illumination pulse of a desired length, and the camera is gated to receive light from the scene for an equal length of time. The camera gating pulse may be simultaneous with the illumination pulse, or it may be delayed relative thereto. The integrated light intensity received at each pixel of the CCD array during the gating pulse is a function of the distance from the camera to the portion of the scene imaged by the pixel. A computer analyzes the light intensity thus received over the entire array and derives range information therefrom.
Range-gated cameras are similarly known in the art. Such camera generally include a gated detector array, working in conjunction with a pulsed or stroboscopic light source, which illuminates a scene. The array may be gated, for example, by coupling a gated intensifier thereto, such as the Intensified Lens System, manufactured by Imco Electro-optics Ltd., Essex, U.K., or by other means well known in the art. The gate timing of the detector array is delayed relative to the light source so that only objects within a desired range of distances from the camera are captured. The camera cannot determine the distances to various objects or different points within the range.